In general, an electrophotographic image forming apparatus such as a laser printer, a facsimile and a photocopier includes a photosensitive body, and a charging roller, a developing roller, a transfer roller and the like installed on the circumference of the photosensitive body. A developing agent supplied from a developing device is moved by voltage applied to a photosensitive body, a charging roller, a developing roller or a transfer roller to form a predetermined image in a printed medium.
For example, a charging roller charges the surface of a photosensitive body with a predetermined voltage, and light scanned in a light exposure unit forms an electrostatic latent image corresponding to print data on the charged surface of the photosensitive body. Then, a developing roller supplies the photosensitive body with a developing agent to develop the electrostatic latent image into a developing agent image. The developing agent image is transferred to a print medium passing between the photosensitive body and a transfer roller by the transfer roller.